Year	Number of
1990	4.97
1991	4.99
1992	5.01
1993	5.12
1994	5.37
1995	5.54
1996	5.67
1997	5.83
1998	5.85
1999	5.92
2000	5.92
2001	6.01
2002	6.11
2003	6.12
2004	6.17
2005	6.29
2006	6.27
2007	6.37
2008	6.45
2009	6.51
2010	6.68
2011	6.85
2012	7.06
2013	7.19
2014	7.47
2015	7.55
2016	7.63